Isothermal characteristics of methane adsorption and changes in the pore structure before and after methane adsorption with high-rank coal

Abstract

The pore structure is an essential factor that influences the isothermal characteristics of methane adsorption of coal, and the pore structure is altered after methane adsorption. In this study, a high-rank coal sample was investigated via methane adsorption isothermal measurement, and changes in the pore structure were studied using low-pressure N2 adsorption and low-pressure CO2 adsorption before and after the methane adsorption. The excess adsorption capacity exhibits a rapid increase at low pressure, reaching a maximum when the test pressure is approximately 8 MPa. Following that, the excess adsorption capacity of the high-rank coal tends to decrease. After the methane adsorption, the pore volume and specific surface area of the micro-, meso-, and macropores increase as compared to those before the methane adsorption, especially for micropores with apertures greater than 0.8 nm and mesopores with apertures below 10 nm. This is mainly caused by high pressure in the methane adsorption, indicating a pressure effect on the pore structure after the methane adsorption. After the methane adsorption, the ratio of pores with various sizes in the high-rank coal is enhanced, but the connectivity for meso- and macropores presents a slight decrease.

Experimental investigation on microstructure fractal characteristics of low-temperature oxidation of gas-bearing coal

“…9 that the mesoporous specific surface area also showed the same trend of firstly increasing and then decreasing. Since the BET method is often used to analyse low-temperature nitrogen adsorption data at relative pressures of 0.05 ~ 0.35, the adsorption in this range is mainly on the outer surface of the pores, so the specific surface area obtained mainly refers to the outer specific surface area of all pores other than those filled with micropores (Li et al, 2023), and the mesopores, as the main pore structure, accounted for nearly 40 times as much of the total pore volume as that of the macropores, which plays a decisive role in the calculation of the BET area, so the…”

Origin Type and Generating Mechanism of Coal Measure Limestone Gas: A Case Study of L1 Limestone Gas in the Taiyuan Formation of the Shenzhou Coal Mine, Eastern Edge of the Ordos Basin, China

“…The test temperature was 30 °C, and 10 test pressures (0.5, 1.0, 2.0, 4.0, 6.0, 8.0, 11.0, 14.0, 17.0, 20.0 MPa) were applied. Then, the Langmuir pressure ( P L ) and Langmuir volume ( V L ) can be obtained by the test data. , …”

“…Then, the Langmuir pressure (P L ) and Langmuir volume (V L ) can be obtained by the test data. 40,41 3.2. Gas Composition and Stable Hydrogen and Carbon Isotope Tests.…”

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“…The characteristics of high gas content and low permeability of medium-and high-rank coals determine that the production mines of medium-and high-rank coals are mostly high-gas and high-risk mines. Studying coal pore shape, connectivity, pore size distribution, pore volume, pore specific surface area, and pore fractal characteristics and their relationship has an important basic role for early warning and prevention and control of gas outburst risks in middle-and high-coal production mines (see Du et al, 2020;Lee et al, 2006;Li et al, 2020;Song et al, 2004;Zhao et al, 2018 and their reference).…”

“…Mangi et al (2020) also study the coal pore structure characteristics and fractal characteristics for untapped coalbed methane (CBM) exploration. Li et al (2020) study the relationship between methane adsorption and the coal structure for high-rank coal. They find that, at low pressure, the excess adsorption capacity increases rapidly and reaches the maximum value when the test pressure is about 8 MPa.…”